1. Field of the Invention
The present invention relates to an image sensor unit including an image sensor for generating an image signal and a filter, and to an image taking apparatus for generating an image signal from a received light from a subject.
2. Description of the Related Art
An image taking apparatus for taking pictures for 24 hours, such as a surveillance camera, has been known. The brightness of a subject to be photographed greatly varies between daytime and nighttime, in particular, in the outdoors. Thus, it is difficult to compensate such a large variation in the brightness by exposure control with a diaphragm used in a conventional camera.
One countermeasure is to use a neutral-density filter and a highly sensitive image sensor. In the daytime, pictures are taken while the neutral-density filter reduces the brightness. In the nighttime, pictures are taken using direct light from a subject while the neutral-density filter is removed to increase relative sensitivity in night photography.
However, the use of such a neutral-density filter requires a mechanism for putting in and taking out the neutral-density filter, resulting in a larger image taking apparatus or an increase in cost.
Another countermeasure is to use a filter that can regulate the amount of transmitted light by the application of a voltage and an image sensor that utilizes such a filter to regulate the light exposure (for example, Japanese Unexamined Patent Application Publication Nos. 10-191181 and 2002-214666). Such a filter may be used in combination with another light control means to decrease the difference in the amount of light between day and night.
However, since the subject is particularly dark in the night photography, only decreasing the difference in the amount of light using such a filter will result in insufficient sensitivity. Thus, some countermeasure that can increase the sensitivity in the night photography and achieve excellent photographing through day and night is desired.